Gaseous Ammonia Removal System

ABSTRACT

A system and method for passive capture of ammonia in an enclosure containing material that gives off ammonia. The invention allows for the passage of gaseous NH 3  through microporous hydrophobic gas-permeable membranes and its capture in a circulated acidic solution with concomitant production of a concentrated non-volatile ammonium salt.

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/314,683, filed Mar. 17, 2010, the contents of which areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to a system and method for the removal of gaseousnitrogen and its conversion to non-volatile nitrogen-containingcompounds to reduce emissions from systems that produce gaseousnitrogen.

BACKGROUND OF THE ART

One of the largest environmental concerns associated with raisingpoultry for production in confined enclosures is the accumulation ofammonia gas (NH₃). Volatilization of NH₃ inside poultry housing oftenresults in an excessive accumulation of NH₃ in the air, which cannegatively affect the health of both workers and birds (Kirychuk et al.,Journal of Occupational and Environmental Medicine 48 (7):741-748, 2006;Ritz et al., Journal of Applied Poultry Research 13:684-692, 2004;Rylander and Carvalheiro, International Archives of Occupational andEnvironmental Health 79 (6):487-490) 2006).

Numerous studies have shown the detrimental effect of high levels of NH₃on bird productivity (Dawkins et al., Nature 427 (6972):342-344, 2004;Ritz et al., supra; Wathes et al., Transactions of the American Societyof Agricultural Engineers 45 (5):1605-1610, 2002; Yahav, Animal Research53:289-293, 2004). Although increased ventilation can lower the NH₃ inpoultry houses to safe levels, it is expensive due to energy costsduring winter months (Moore et al., 1995, Journal of EnvironmentalQuality, Volume 24, 293-300). Since NH₃ cannot be effectively containedwithin the house structure, NH₃ emissions may contribute to airpollution, atmospheric deposition, and health concerns for near-byresidents (Nahm, 2003, World's Poultry Science Journal, Volume 59,77-88; Wheeler et al., 2006, Transactions of the American Society ofAgricultural Engineers, Volume 49(5), 1495-1512; Williams et al., 1999,Reviews of Environmental Contamination and Toxicology, Volume 162,105-157; Wing and Wolf, 2000, Environmental Health Perspectives, Volume108(3), 233-238).

Ammonia levels as low as 20 ppm have been found to compromise the immuneand respiratory systems of chickens, making them more susceptible todisease. High levels of ammonia also negatively affect their feedconversion and weight gain. As a result of all these negative impacts onperformance, recommended ammonia concentrations in poultry barns shouldbe well below 25 ppm.

High levels of ammonia may also pose a risk to the health ofagricultural workers in chicken rearing facilities; exposure to ammoniacan irritate the respiratory tract and eyes, even at low levels.Therefore, the Federal Occupational Safety and Health Administration(OSHA) permissible worker exposure limit for ammonia is 50 ppm over an8-hour period and the American Conference of Governmental IndustrialHygienists (ACGIH) has established a short-term (15-min) exposure limitof 35 ppm.

Current NH₃ abatement technologies used in livestock houses rely on theventilation systems and treatment of the exhaust air after leaving thehouse to remove nitrogen. Typically such systems are large requiring alot of power that allows for an exchange range from 275 to 451 cubicfeet of air per second depending on ambient temperatures (colder andwarmer, respectively), assuming an average weight per broiler of 1.3 kgand 20000 broilers per house (American Society of Agricultural andBiological Engineers, Design of Ventilation Systems for Poultry andLivestock Shelters, ASABE Standard Practices, ASAE EP270.5 December 1986(R2008), 1986). Such massive ventilation allows for the dilution ofindoor ammonia levels and it does increase the removal amounts ofammonia from poultry facilities. However, ammonia releases from suchfacilities in this manner to the atmosphere is expensive in the coldermonths and throughout the year can cause environmental problems, such asacid precipitation, fine particulate matter formation (particulatematter with an aerodynamic diameter less than ten microns in size), andnitrogen deposition into aquatic systems. The accumulated effects ofventilation contribute to a reduction in the quality of life and raisehealth concerns for near-by residents.

A second strategy includes treating the NH₃ in the exhaust air fromenclosures using scrubbing or filtration techniques, thus preventing NH₃release into the environment. This technique consists of forcing theventilated air through an NH₃ trap, such as an acidic solution(scrubbers), or through a porous filter with nitrifying biofilms thatoxidize NH₃ to nitrate (biotrickling or organic filters) (Chen et al.,Chemosphere 58 (8):1023-1030, 2005; Melse and Ogink, Transactions of theASAE 48 (6):2303-2313, 2005; Ndegwa et al., Biosystems Engineering100:453-469, 2008; Pagans et al., Chemical Engineering Journal 113(2-3):105-110, 2005). The process is costly in winter months when it isnecessary to heat enclosures to maintain production. In addition, recentresearch has shown that NH₃ concentrations close to the litter surface(<20 cm), where the birds are exposed, can be up to one order ofmagnitude higher than in the bulk house air.

The third technology is to selectively pull and treat the air near thelitter surface, where NH₃ levels are more concentrated, using dedicatedventilation systems independent of the house ventilation system (Lahavet al., Water Air Soil Pollution, Volume 191, 183-197, 2008). Asignificant departure from the methods described above is the concept ofremoving NH₃ using manifolds that extract only the air close to thelitter independent of the house ventilation system. These systemsrequire redundancy, additional positive air extraction equipment and arethus not cost effective.

A fourth form of abatement is to add chemical amendments directly to thepoultry litter to prevent NH₃ volatization, without the need ofadditional ventilation to move NH₃. These amendments act by eitherinhibiting microbial transformation of urea or uric acid into NH₃ or byacidifying and neutralizing it. Several chemical amendments have beenwidely used for their ability to control or reduce NH₃ release frompoultry litter and manure, such as AL₂(SO₄)₃.14 H₂0 (Al+Clear®), NaHSO₄(PLT®), and acidified clays (Poultry Guard®) (Cook et al., Journal ofEnvironmental Quality 37:2360-2367, 2008; Moore et al., 1995, supra;Moore et al., Journal of Environmental Quality 29:37-49, 2000; Shah etal., Poultry litter amendments, edited by N. C. C. E. Service. Raleigh,N.C.: North Carolina State University, 2006). Although N is conservedunvolatilized in the poultry litter, NH₃ is not recovered as a separateproduct as with the scrubbing techniques. Recovery of NH₃ is a desirablefeature because it can be exported off the farm, solving problems of Nsurpluses in concentrated poultry production regions.

Conservation and recovery of nitrogen (N) is also important inagriculture because of the high cost of producing and acquiringcommercial NH₃ fertilizers. Thus, there is a desire to improvetechnologies for abating NH₃ emissions from confined poultry operationsby capturing and recovering nitrogen.

While, various systems have been developed for removing NH₃ from animallitter, there still remains a need in the art for different abatementsystems that removes NH₃ from gaseous nitrogen producing systems andrecovers the N in a concentrated purified form, but is not dependent onintense air movement.

The present invention, different from prior art systems, provides suchsystems using hydrophobic gas-permeable membranes and circulated acidicsolutions to produce concentrated ammonium salt.

SUMMARY OF THE INVENTION

It is therefore ah object of the present invention to provide a systemfor at least reducing levels of NH₃ in an enclosed area and recovering Nin a purified concentrated form.

Another object of the present invention is to at least reduce the levelof NH₃ in an enclosure using systems that do not require large capacityairflow handling systems.

A still further object of the present invention is to provide a systemfor at least reducing the levels of NH₃ in an enclosed space usingsystems that capture NH₃ in a circulated acidic solution with theconcomitant production of a concentrated ammonium salt.

A still further object of the present invention is to provide a systemfor at least reducing the levels of NH₃ in an enclosed area usingsystems that remove NH₃ through the use of microporous, hydrophobic,gas-permeable membranes.

Another object of the present invention is to provide a system for atleast reducing the levels of NH₃ in an enclosed area using systems thatremove NH₃ through the use of microporous, hydrophobic gas-permeablemembranes and chemical amendment of animal litter used in the enclosedspace.

A still further object of the present invention is to provide a systemfor at least reducing the levels of NH₃ in an enclosed space containinganimal litter wherein in said litter includes a chemical which enhancesNH₃ release from the litter.

Another object of the present invention is to provide a system for atleast reducing the levels of NH₃ in a composting system and recovering Nin a purified concentrated form.

Another object of the present invention is to provide a method for atleast reducing NH₃ in an enclosed space using a system that does notrequire large capacity airflow handling systems.

A still further object of the present invention is to provide a methodfor at least reducing NH₃ in ah enclosed space using a system thatcaptures NH₃ in a circulated acidic solution with the concomitantproduction of a concentrated ammonium salt.

A still further object of the present invention is to provide a methodfor at least reducing NH₃ in an enclosed space using a system havingmicroporous, hydrophobic, gas-permeable membranes.

Another object of the present invention is a method for at leastreducing NH₃ in an enclosed space using a system having microporous,hydrophobic gas-permeable membranes and a chemical amendment of ananimal litter used in the enclosed space wherein said amendmentincreases the release of NH₃ from the litter.

A still further object of the present invention is to provide a methodfor at least reducing NH₃ in a composting system using a system havingmicroporous, hydrophobic gas-permeable membranes.

Further objects and advantages of the invention will become apparentfrom the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional drawing of ammonia capture using hydrophobicgas-permeable tubing 8 and shows membrane manifold system 17 includingmembrane 8, membrane outer surface 8A, membrane inner surface 8B,membrane pores 9, hollow interior of tubular membrane 10, membraneassembly entry opening 40 and membrane assembly exit 42. Ammonia gas(NH₃) permeates through hydrophobic membrane 8 walls with micron-sizedpores 9, where it combines with the free protons (H⁺) in the acidsolution 3 to form non-volatile ammonium ions (NH₄ ⁺).

FIG. 2 is a diagram showing a basic configuration of system 20 for NH₃recovery showing membrane system or assembly 15 having acid tank 1, acidsolution 3, fluid pump 4, hydrophobic, microporous, gas permeablemembrane 8 in a tubular configuration, pump intake flow line 11 and pumpdischarge flow line 12, a first membrane assembly entry opening 40 and amembrane assembly exit opening 42, and further showing enclosure/chamber22, and NH₃, emitting source 6.

FIG. 3 is a drawing of a chamber used to determine the feasibility ofusing ePTFE gas-permeable membrane system to capture and recover NH₃from poultry litter having gas permeable membrane 8, pump intake flowline 11 and pump discharge flow line 12, a membrane assembly entryopening 40 and a membrane assembly exit opening 42, and further showingenclosure/chamber 22, and NH₃, emitting source 6.

FIGS. 4(A-C) are scanning electron micrograph images for three differentePTFE tubular membranes showing different pore structures. All imagesare taken at 1000× magnification, and the scale bar is equivalent toapproximately 20 μm in length. All three tubular membranes were used forthe first/experiment, while only ePTFE Type B (FIG. 4B) was used forsubsequent experiments.

FIGS. 5 A-C are drawings showing positioning of the ePTFE tubularmembranes 8 with respect to the emitting source 6 (poultry litter)surface in the Above (FIG. 5A), On (FIG. 5B), and Under (FIG. 5C)treatments. The black tubing represents the impermeable Tygon® tubingand the light tubing represents the gas-permeable ePTFE tubing. Thedashed box surrounding the ePTFE in FIG. 5C represents the nylon meshpocket that supported the ePTFE tubing under the litter.

FIG. 6 A is a graph which shows the mass of NH₃ recovered in the acidicsolution and FIG. 6B is a graph which shows NH₄-N remaining in thepoultry litter (PL) from chambers possessing three different types ofePTFE tubular membranes. The controls (▾) were run for both the acidicsolution (A; acid without poultry Utter) and poultry litter (B; chamberwithout ePTFE NH₃ capture). All data points are the mean of duplicatechambers.

FIG. 7 A is a graph showing the mass of NH₃ recovered in the acidicsolution and FIG. 7B is a graph showing NH₄-N remaining in the poultrylitter (PL) from chambers comparing the effect of membrane height fromlitter surface. The controls (▾) were run for both the acidic solutionand poultry litter as described in FIG. 6. All points are the mean ofduplicate chambers. The bar in the upper right corner of each graphrepresents the LSD_(0.05) value for the NH₃ recovered in the acidicsolution (approximately 27.992) and NH₄-N remaining in the litter(approximately 63.657).

FIG. 8 is a graph showing the mass of NH₃ in the acidic solution fromchambers amended with (approximately 5% w/w) or without urea as anitrogen source to simulate the nitrogen input to the litter in apoultry house. A control (▾) was run for the acidic solution (withoutpoultry litter). All points represent mean values of duplicate numbers.

FIG. 9A is a graph showing the mass of NH₃ recovered in the acidicsolution and FIG. 9B is a graph showing NH₄-N remaining in the poultrylitter (PL) from chambers amended with hydrated lime (Ca(OH)₂). Day 1litter values in FIG. 9B represent initial samples that remained on thebench-top for one day prior to analysis to determine the rapid releaseof NH₃ from the litter. The controls (▾) were run for both the acidicsolution and poultry litter as described. All points represent the meanof duplicate chambers, and the error bar in the upper right hand cornerof the graphs represents the LSD_(0.05) value for the NH₃ recovered inthe acidic solution (approximately 50.711) and NH₄-N remaining in thelitter (approximately 123.19).

FIG. 10 is a cross section schematic diagram of ammonia (NH₃) capturesystem 20 using hydrophobic gas-permeable flat membrane. Shown in thediagram are acid solution (NH₃ sink) 3, acid tank 1 for acid solution,intake flow line 11, pump discharge flow line 12, fluid pump 4, pumpintake end 4A, pump discharge end 4B, and enclosure or barn 22, NH₃emitting source (Poultry Litter, for example) 6, membrane assembly 15including trough covered with flat membrane 7 exposed to air with NH₃hydrophobic, gas-permeable flat membrane outer surface 8A, membranepores 9, acid solution 3 flowing within trough 7, and membrane air space16 between membrane inner surface 8B and surface of acid solution 3flowing within trough 7, membrane assembly entry opening 40 and membraneassembly exit opening 42.

FIG. 11 is a graph showing rapid reduction of gaseous ammonia from airwithin enclosures using a flat membrane prototype with poultry litter.Various concentrations of NH₃ in the air (approximately 0 to 6 hours)were established using different rates of hydrated lime (Ca(HO)₂)applied to the emitting source (poultry litter) at time=0.

FIG. 12 is a graph showing recovery of ammonia from poultry litter usinga flat membrane prototype. The litter was treated with different ratesof hydrated lime (Ca(HO)₂) to increase the concentration of NH₃ in theair. The dashed horizontal line represents the mass of NH₄-N initiallypresent within the poultry litter. Error bars represent the standarddeviation of duplicate experiments.

FIG. 13 is a cross section schematic diagram of ammonia (NH₃) capturesystem 20 from poultry litter using a membrane system 15 having ahydrophobic gas-permeable flat, membrane manifold system 17 includingmultiple troughs 7 connected in series. Shown in the diagram are acidsolution (NH₃ sink) 3 Acid tank/reservoir 1 for acid solution, intakeflow line 11, discharge flow line 12, fluid, pump 4 with intake end 4Aand discharge end 4B, enclosure or barn 22, NH₃ emitting source (PoultryLitter, for example) 6, trough 7 covered with flat membrane 8 exposed toair with NH₃ hydrophobic, gas-permeable membrane 8 in flatconfiguration, acid solution 3 flowing within trough 7, and membrane airspace 16 between inner membrane surface and surface of acid solution 3flowing within trough 7. Also shown are membrane assembly entry opening40 and membrane assembly exit opening 42, acid flow pipe 18.

FIG. 14 is an aerial view schematic diagram of ammonia (NH₃) capturesystem from using multiple hydrophobic gas-permeable flat membranetroughs 7 connected in parallel. Shown in the diagram are acid solution(NH₃ sink) 3, acid tank 1 for acid solution, intake flow line 11,discharge flow line 12, fluid pump 4 with intake end 4A and dischargeend 4B, enclosure or barn 22, NH₃ emitting source 6, hydrophobicgas-permeable flat membrane troughs 7, acid flow pipes 18, and membraneassembly entry opening 40 and membrane assembly exit opening 42.

FIG. 15A is a three dimensional schematic diagram of plastic trough 7with flat gas permeable membrane 8 to remove NH₃ from the air acidsolution 3, membrane assembly entry opening 40 and membrane assemblyexit opening 42, and 15B is a cross section schematic diagram of thesame trough with flat gas permeable membrane outer surface 8A, membranepore 9, and membrane air space 16 between inner membrane surface 8B andsurface of the acid solution 3.

DETAILED DESCRIPTION

The present invention recovers N in a concentrated purified form, but isnot dependent on intense air movement. The invention is an ammonia gascapture system 20 that includes the passage of NH₃ through a membraneassembly 15 that includes at least one microporous hydrophobicgas-permeable membrane 8 and the capture of NH₃ in a circulated acidsolution 3 with concomitant production of a concentrated-ammonium salt.Once NH₃ is in contact with the acid solution 3 it reacts with freeprotons (H⁺) to form non-volatile ammonium (NH₄ ⁺) salt, which isretained and concentrated in the acid solution 3 (FIGS. 1 and 10).

Modern animal production is an extremely sophisticated business and themanagement, treatment, purification, and appreciation of its by-productsshould also be so. As the practice of intensive production in enclosedareas, such as for example, stables, barns, poultry houses, penfacilities, etc., grows there is an increasingly urgent need foreffective and affordable alternatives for management of nutrientby-products.

The removal and recovery of NH₃ is a desirable feature because it can beexported off the farm which solves the problems of nitrogen surpluses inconcentrated farm animal production regions. The present invention usesgas-permeable membranes that are placed inside an enclosure housing farmanimals for production to recover nitrogen in a concentrated purifiedform and is not dependent on intense airflow. According to ASABEstandards, required Ventilation ranges from 275 to 451 cubic feet of airper second depending on ambient temperatures (colder and warmer,respectively), assuming an average weight per broiler of 1.3 kg and20,000 broilers per house (American Society of Agricultural andBiological Engineers, Design of Ventilation Systems for Poultry andLivestock Shelters, ASABE Standard Practices, ASAE EP270.5 December 1986(R2008), 1986). As shown in FIGS. 1, 2, and 10, the invention allows forthe passage of gaseous NH₃ through microporous hydrophobic gas-permeablemembranes 8 and its capture in a circulated acid solution 3 withconcomitant production of a concentrated non-volatile ammonium salt.Once the NH₃ is in contact with the acid solution 3, it reacts with freeprotons (H⁺) to form the non-volatile ammonium (NH₄ ⁺) salt, which isretained and concentrated in the acid solution 3.

Hydrophobic, gas-permeable membrane 8 includes, for example,polypropylene (Shindo et al., Gas transfer process with hollow fibermembrane. Japan: Mitsubishi Rayon, Co., Ltd., 1981),polyethylene/polyurethane composites (Lee and Rittmann, Water ScienceTechnology 41:219-226; 2000), or polytetrafluoroethylene (PTFE) (Blet etal, Analytica Chimica Acta, Volume 219, 309-311, 1989). Membrane 8 canbe tubular or flat as shown in FIGS. 2 and 10. Semi permeable membrane 8includes but is not limited to hydrophobic gas permeable hollow fibermembranes 8 (FIGS. 1 and 2) made from polypropylene (Shindo et al., Gastransfer process with hollow fiber membrane. Japan: Mitsubishi Rayon,Co., Ltd., 1981), and polyethylene/polyurethane composites (Lee andRittmann, 2000, supra), silicone rubber (Carlson, R. M. 1978. AutomatedSeparation and Conductometric Determination of Ammonia and DissolvedOrganic Carbon. Anal. Chem. 50: 1528-1531), polysulfone,polytetrafluoroethylene (PTFE) (Blet et al., supra) or expandedpolytetrafluoroethylene (ePTFE). See also U.S. Pat. No. 5,474,660 andNo. 5,071,561 herein incorporated in their entirety by reference.

FIGS. 2 and 10 are schematic diagrams showing the interior of anenclosure 22 and the ammonia capture system 20 of the invention, NH₃emitting source (poultry litter, for example) 6 is soiled with wasteproducts that primarily include urine and feces and possibly undigestednitrogen-containing feed. The nitrogen present in these waste materialsis located on the floor 26 of enclosure 22 and ammonia gas generatedfrom said urine, feces and/or food permeates the enclosure. A membraneassembly 15 includes a microporous, hydrophobic, gas-permeable membrane8 that is disposed within enclosure 22 and is in closed-loopcommunication via fluid pump 4 with an acid solution 3 contained inreservoir 1. Membrane 8 includes an outer surface 8A, and inner surface8B, membrane pores 9, and membrane assembly entry opening 40 and amembrane assembly exit opening 42.

For purposes of the present invention the term litter is defined as anymaterial put on the bottom surface of an enclosed space that can bebedding for an animal, for example and/or contains waste productsincluding urine, feces and possibly undigested nitrogen-containing feed.

For purposes of the present invention, the term enclosure is defined asany structure having an area that has been enclosed such as for example,stables, barns, poultry houses, animal pens, composting bins, anaerobicdisgesters, etc.

Furthermore, for purposes of the present invention, ammonia capturesystem 20 can be used to capture ammonia from composting. For purposesof the present invention, the term composting is defined as anybioxidative process involving the mineralization and partialhumification of organic matter leading to stabilized usable substancescalled compost. During the composting process the simple organiccompounds are mineralized and metabolized by the microorganismsproducing CO₂, NH₃, H₂O, organic acids, and heat

The membrane assembly 15 including membrane 8 functions as a passivegetter for ammonia gas and as the gas is captured, production of moregas from non-volatile NH₄ occurs until all or substantially all of theNH₄ is converted to NH₃.

The membrane 8 itself is a tubular or flat microporous, hydrophobic,gas-permeable membrane 8 having membrane pores 9. The tubular membrane 8is defined as an endless circumferential material having an outersurface 8A and an inner surface 8B (see FIG. 1). The inner surface 8Bdefines a hollow interior 10 (FIG. 1). Thus the permeable membrane 8allows for the diffusion of ammonia gas concentrated outside the outersurface 8A to diffuse through the membrane 8 to the hollow interior 10.Another embodiment of membrane 8 is the use of a flat, microporous,hydrophobic, gas-permeable membrane (FIG. 10) such as, for example,PTFE, ePTFE, polypropylene, polypropylene-backed ePTFE laminates,nylon-backed ePTFE laminates, and polyethylene-backed ePTFE laminates.Membrane 8 is defined by an upper and a lower surface, each having anouter 8A and inner 8B surface. The flat membrane is stretched over atrough 7 which contains flowing acid solution 3 with an air space 16between membrane 8 and acid solution 3. It operates by allowing for thediffusion of ammonia gas concentrated outside the outer surface 8A todiffuse through membrane 8 to the interior into membrane air space 16.

Hollow, tubular, gas-permeable membranes typically have wall thicknessranging from 0.1-2.0 mm, inner diameter ranging from 0.3-100 mm, bubblepoint ranging from 3−300 kPa, and porosity ranging from 40-80%. Thetubular membranes can be assembled in modules with several tubingsparallel to each other and a common intake and outtake. Flat,gas-permeable membranes are typically defined by their membranethickness (ranging from 0.001-0.2 mm), bubble point (ranging from 3−300kPa), and porosity (ranging from 40-80%). Flat membrane surface area wasequivalent to approximately 11 to 14% of the enclosure surface area inboth the bench-scale and field-scale experiments.

The closed loop delivery system for delivering acid from acidtank/reservoir 1, in FIGS. 2 and 10, to the hollow interior 10 oftubular membrane 8 or to membrane airspace 16 in trough 7 of membraneassembly 15 including flat membrane 8 is composed of fluid pump 4 havingan intake end 4A and discharge end 4B and at least two hollow flow lines11 and 12 having distal and proximal ends. Discharge flow line 12 hasone end in fluid communication to the discharge end 4B of the fluid pump4. Intake flow line 11 has a first end attached to the intake end 4A offluid pump 4 and a second end in said reservoir 1 for delivering acidsolution 3 to said membrane system 15.

For purposes of the present invention, the term acid tank/reservoir isdefined as any size, nonreactive container for the storage of acid usedin the present invention.

As shown in FIGS. 2 and 10, the acid solution 3 not only is a reactantmaking the conversion of NH₃ to NH₄ solid salts but also acts as asweep, via the mechanical action of fluid pump 4, moving the salts toreservoir 1. These salts then can be used a fertilizer. Acids that canbe used in the method of the invention include organic acids such ascitric, oxalic, lactic, etc., mineral acids such as sulfuric,hydrochloric, nitric, phosphoric, for example, or a mixture of bothmineral and organic acids or their precursors, such as sodium bisulfate,sulfur, corn silage, molasses, and carbohydrates or mixtures thereofetc. Approximately 1 Normal acid solutions are preferred.

Gaseous nitrogen producing can be treated by the addition of chemicalswhich enhance the volatilization of NH₃ from the litter. An example isan alkali chemical that converts NH₄-N to NH₃ according toammonium-ammonia reaction: NH₄ ⁺→NH_(3↑)+H⁺. Using calcium hydroxide(i.e. lime) as an example, the following equation defines the reaction:Ca(OH)₂+2NH₄ ⁺→2NH_(3↑)+Ca²⁺2H₂0. Any chemical which will increase thevolatilization of NH₃ from the litter can be used in the practice ofthis invention, such as calcium hydroxide, magnesium hydroxide, calciumoxide, magnesium oxide (and mixtures thereof), dolomitic lime, sodiumhydroxide, and potassium hydroxide. The amount of alkali to applydepends on the degree of ammonia removal desired (see FIG. 12). Usinglime as an example, a typical amount of ˜2% (w/v) used for thedisinfection of the litter will be sufficient to volatilize at least 80%of the ammonia from poultry litter. Lower amounts of lime in the rangeof 0.1-0.5% (w/v) will volatilize approximately 5 to 60% of the ammoniain the poultry litter. A simple test measuring ammonium in the poultrylitter in KCl extracts (Peters et al., Ammonium nitrogen, p. 25-29, InJ. Peters, ed. Recommended Methods of Manure Analysis. University ofWisconsin Extension, Madison, Wis., 2003) can be used to determine therate of lime application for optimum ammonia volatilization. In thistest, lime is applied at 3 to 5 rates between 0 and 2% (w/v), and thedifference in KCL-extractable ammonium from the litter before and afterlime application is taken as N loss.

The following examples are intended only to further illustrate theinvention and are not intended to limit the scope of the invention whichis defined by the claims. Poultry litter is used as a model to exemplifythe system of the present invention. The system can be used for anyenclosed space where NH₃ is produced and accumulated.

Example 1

This example includes four experiments for the process configurationwherein an acid solution is contained in an acid tank and wascontinuously recirculated into a chamber containing poultry litter (SeeFIG. 2). Once inside the chamber, the acid was contained inside amicroporous, hydrophobic gas-permeable, tubular membrane 8 allowing forthe passage of NH₃ gas emitted by the litter and subsequent recovery andconcentration of the N as an ammonium salt.

FIG. 3 shows a 2-L, polyethylene terephthalate (PET) plastic, wide-mouthjar 18 cm (h)×12 cm (dia) with a threaded polyethylene lid (Cole-Palmer,Vernon Hills, Ill., USA). There were a total of five ports in the lid ofthe chamber, two for acid inflow-outflow, one for venting air, throughtubing with glass wool, to ensure ambient pressure and aerobicconditions inside the chamber, and the remaining ports, allowedheadspace air sampling (only the inflow-outflow ports are depicted).Tygon tubing (approximately 4.75 mm I.D., 6.35 mm O.D., 0.8 mm wallthickness) was used for the inflow and outflow lines outside of thechamber. The chamber contained approximately 300 grams of poultry litterwith a height inside the chamber of about 5 cm. The acid tank (FIG. 2)consisted of a 500 ml glass flask containing approximately 300 ml 1 NH₂S0₄. A peristaltic Manostat pump (Cole-Parmer, Vernon Hills, II., USA)was used to continuously pump the acid through the tubular membranesinside the chamber and back into the acid tank using flow rates ofapproximately 70-80 ml day⁻¹. The flow rate was selected from previouslaboratory experiments that indicated that low (approximately 70-80 mLper day) or high (approximately 240-320 mL per day) flow rates of theacidic solution through the membrane system did not significantly affectNH₃ recovery (data not shown). Therefore, the lower flow rate was usedto prolong the life of the pump tubing.

Expanded polytetrafluoroethylene (ePTFE)(Phillips Scientific Inc., RockHill, S.C.) was used in the interior of the chamber for NH₃ capture. Thelength of the tubing used in all experiments was approximately 66 cm.Characteristics of the ePTFE tubing and scanning electron micrographsfor each of the three types of ePTFE tubing used in these studies areshown in Table 1 and FIG. 4, respectively.

TABLE 1 Physical characteristics of the different ePTFE tubularmembranes used. Inner Diameter Wall Thickness Bubble Point Type (mm)(mm) (kPa) A 4.00 0.25 34.5 B 5.25 1.00 241.3 C 8.75 0.75 206.8

Four experiments were performed to test the feasibility of using ePTFEtubular membranes in conjunction with an acidic solution to capture andrecover NH₃. The first experiment determined the general applicationusing three ePTFE membranes with different physical characteristics. Thesecond experiment determined if NH₃ recovery could be enhanced withdifferent placements of the membranes with respect to the littersurface. The third experiment determined the maximum capture capacity ofthe membranes by addition of excess urea to the poultry litter. Thefourth experiment evaluated if the release of NH₃ from the litter couldbe recovered quickly through the use of hydrated lime treatments incombination with the use of membrane technology.

In all experiments, approximately 300 mL of 1 N H₂SO₄ was circulated ata flow rate of approximately 70-80 mL per day. Duplicate experimentswere run for a total of 21 days. Add solution was sampled daily andheadspace air (approximately 15-20 volumes) was sampled weekly. The pHof the acidic solution was monitored using pHydrion Insta-Chek 0-13litmus paper (Micro Essential Laboratory, Brooklyn, N.Y.). For the airsampling, headspace air was evacuated from the chamber and the NH₃ wastrapped in 1N H₂SO₄ via glass impingers according to Poach et al.(Journal of Environmental Quality, Volume 33, 844-851, 2004). Afterheadspace evacuation, lids were removed, the litter was mixed usinggloves, and a representative grab sample (about 12-15 grams) was takenprior to resealing the lid. Liquid samples were capped and stored atabout 4 degrees G and litter samples were stored at about −20 degrees C.until analysis. Duplicate control chambers were set up containing lifterbut no ePTFE tubing and sampled weekly to determine headspace NH₃ andlitter characteristics without an NH₃ removal system. In addition, a500-mL Erlenmeyer flask was set up as an acid tank control (notconnected to any chamber) that was sampled at the same time as the otheracid solution samples.

The bedding material that constituted the base of the broiler litter inall experiments was wood chips. Broiler litter used for the experimentswas collected from a 25,000 bird broiler house in Lee County, SouthCarolina. At the time of sampling, the house was empty and between thesecond and third flock (five flocks per year). Two large compositelitter samples were taken in two transects along the center section ofthe house (between water lines), and placed in 160-L containers. Thecontainers were sealed and transported to the laboratory. Approximately15 gram portion of the litter was passed through a 5.8 mm sieve andplaced in cold storage (about −65 degrees C.) prior to laboratoryexperiments. The properties of the litter can be seen in Table 2 below.The starting weight of poultry litter was approximately 200 grams foreach chamber, and all experiments were performed at ambient pressure andtemperature room conditions.

TABLE 2 Poultry Litter properties Parameter Unit Value^([a]) MoistureContent^([b]) % 19.7 Volatile Solids^([c]) % 78.6 pH 9.06 Total N^([d])g kg⁻¹ 26.3 NH₄—N^([d]) g kg⁻¹ 13.7 Total C^([d]) g kg⁻¹ 352 ^([a])Meanfor triplicate litter samples (n = 3) ^([b])Percent of total mass asmeasured after drying for 24 hours at 105° C. ^([c])Percent of TotalSolids, as measured after ashing at 550° C. for 30 mins. ^([d])Dryweight basis

All liquid samples were analyzed for NH₄-N according to Standard Method4500-NH₃ G (APHA, 1998). Total Kjeldahl N (TKN) in solid samples wasdetermined in digestion extracts using H₂SO₄ (Gallaher et al., SoilScience Society of American, Volume 4, 887-8891976). The NH₄-N and NO₃-Nwere extracted from the litter using a 60:1 2M KCl: litter mixture thatwas shaken (about 200 rpm) for about 30 minutes followed by gravityfiltration through Whatman filter paper, size 42 (Whatman InternationalLtd., Maidstone, England) (Peters et al., Ammonium Nitrogen, P. 25-29,In. J. Peters (ed.) Recommended Methods of Manure Analysis. Universityof Wisconsin Extension, Madison, Wis., 2003). All NH₄-N,NO₃-N, and TKNanalyses in solid samples were determined by colorimetry using theAutoAnalyzer II (Technicon, 1977; Technicon Instruments Corp.,Tarrytown, N.Y.). Elemental analysis for total C and N was done by drycombustion (Leco Corp., St. Joseph, Mich.). All litter analyses werereported on a dry-weight basis. Moisture content of the poultry litterwas determined by oven drying/the litter at about 105 degrees C. toconstant weight. The dried sample was ignited in a muffle furnace atabout 550 degrees C. for about 30 minutes to determine volatile solids(VS). Litter pH was measured electronically using a combination pHelectrode at a 5:1 deionized water:litter ratio. Data were statisticallyanalyzed by means and standard errors (proc MEANS), linear regression(proc REG), and analysis of variance (proc ANOVA), and least significantdifference at a 0.05 probability level (LSD_(0.05)) for multiplecomparisons among means with SAS version 9.2 (SAS, 2008).

Experiment 1

The first experiment was designed to determine the general feasibilityof using ePTFE tubular membranes on the recovery of NH₃ released frompoultry litter. Three different ePTFE tubings were tested (Table 1 andFIG. 4), and identified as A, B, or C; distinguished by the followingproperties. Tubing A possessed an inner diameter of 4.00 mm, a wallthickness of 0.25 mm, and a bubble point of 34.5 kPa. Tubing B possessedan inner diameter of 5.25 mm, a wail thickness of 1.00 mm, and a bubblepoint of 241.3 kPa. Tubing C possessed an inner diameter of 8.75 mm, awall thickness of 0.75 mm, and a bubble point of 206.3 kPa. The membranetubing inside the chamber had the same length (approximately 66 cm) butvaried in terms of wall thickness, pore size, and bubble points.Placement of the ePTFE tubing was approximately 5 cm above the littersurface (shown in FIG. 5A).

The membrane system recovered about 96% of the NH₃ lost from the litterduring the 21 day evaluation (FIG. 6, Table 3). FIG. 6A shows a steadylinear (y=11.18×+21.68, r²=0.8764) increase in NH₃ accumulation in theacidic solution during the study as NH₃ was slowly released from thelitter, as compared to the control where no NH₃ accumulated in theacidic solution. The three evaluated membranes performed similarly, withno significant difference in the total mass of NH₄-N accumulated in theacidic solution by the end of the experiment (Table 3). On the average,the total NH₃ recovered in the acidic solution was approximately 267.0mg, compared to approximately 278.4 mg lost from the litter during thesame period, resulting in approximately 96% mass recovery. The NH₃capture rate, on a surface area basis, was approximately 1.37, 1.29, and0.70 g m⁻² d⁻¹ for types A, B, and C, respectively. As the NH₃ was beingrecovered from the air with the membranes, the NH₄-N contained in thelitter decreased accordingly; on the other hand, the NH₄-N content inthe control treatment changed little (approximately 20%) throughout theexperiment (FIG. 6B). This suggests that the removal of the NH₃ from thechamber using membranes allowed for a change in equilibriumconcentration of ammoniacal-N in the litter. The high removalefficiencies obtained in this experiment showed that the use of NH₃gas-permeable membranes for poultry litter application is feasible.

TABLE 3 Physical properties, mass balance and NH₃ capture rates of thethree ePTFE tubular membranes after 21 days. Total NH₄—N PropertiesCaptured in Total NH₄—N Surface Area S/V Acidic Lost from NH₄—N TYPE(cm²) (cm²/cm⁻³)^(a) Solution (mg)^([b]) Litter (mg)^([d]) Recovery % A83.2 10.0 240.2 (3.9)^([c]) 267.2 (4.0) 89.9 B 108.9 7.6   293 (5.2)287.8 (3.7) 102.1 C 181.5 4.6 266.8 (5.4) 280.1 (6.4) 95.3 Control n/an/a  0.0 102.1 (1.4) 0.0 LSD_(0.05) ^([e]) 54.02 69.33 ^([a])Membranesurface to volume ratio. ^([b])Total NH₄—N measured in the acid trapafter 21 days incubation ^([c])Mean (standard error of mean) forduplicate samples (n = 2). ^([d])Total NH₄—N in the litter at the end ofexperiment calculated by subtracting NH₄—N content on day 21 frominitial NH₄—N content on day 0. ^([e])Least significant difference

Experiment 2

The second experiment was designed to determine if placement of theePTFE tubing with respect to the litter surface had an effect on NH₃recovery. Type B ePTFE tubing (Table 1) was used for this experiment.The tubing was placed inside the chamber in the following threepositions (FIG. 5): (A) Above: approximately 5 cm above the littersurface; (B) On: laying directly on the litter surface, and (C) Under:below the litter and inside a pocket made of 300-μm nylon mesh (KrystalKlear Filtration, Winamac, Ind.) to support the tubing under the weightof the litter.

The relative position of the tubular membranes (above, on, or under thelitter) did not significantly affect the total mass of NH₃ recovery bythe system (FIG. 7A, p=0.4776) nor the mass of the NH₄-N remaining inthe litter after volatilization (FIG. 7B, p=0.7908). Therefore, theresults of the three treatments were pooled together to perform a weeklymass balance of the NH₄-N in the chambers (Table 4). In terms ofrecovery efficiency, approximately 81.5% of the NH₄-N was recovered bythe end of the third week. The NH₃ volatilized from the litter can movedown and below the litter layer and be effectively recovered, as shownin the “under” treatment in FIG. 7A. This provides flexibility in futuremembrane treatment system design. For example, membrane manifolds may beplaced below the bedding, or under caged production, thus minimizingexposure of birds to NH₃. Our results also show that abovegroundplacement of membrane manifolds is equally effective at recovering NH₃from the litter, and these manifolds could be placed in grids near thesurface or along waterer/feeder: lines, or even placed on the buildingwalls.

TABLE 4 Weekly mass balance and percent recovery of NH₃ from pooledpoultry litter samples from the three chambers with ePTFE tubularmembranes at varying heights with respect to litter surface NH₄—N NH₄—NMass NH₄—N Mass Sampling Content of Loss from Recovered in NH₄—N TimeLitter Litter Acid Trap Recovery (days) (mg kg⁻¹) (mg)^([b]) (mg) (%) 0 1369.2 (9.2)^([a]) 0 0 0 7 758.3 (8.2) 211.4 (4.1) 172.3 (3.3) 81.5 14766.7 (9.9) 208.4 (6.1) 199.7 (3.7) 95.8 21 791.7 (7.2) 207.3 (4.0)230.0 (3.6) 110.9 ^([a])Mean (standard error of the mean) of duplicate2M KCl extractions of litter from the three treatments in experiment 2(n = 3) ^([b])Calculated by subtracting mass of NH₄—N at that samplingtime from initial mass of NH₄—N in the litter

Current NH₃ abatement technologies used in livestock houses rely on theventilation systems and N treatment of the exhaust air after leaving thehouse (Melse and Ogink, Transactions of the ASAE, Volume 48(6),2302-2313, 2005; Ndegwa et al., Biosystems Engineering, Volume 100,453-469, 2008), but recent research has shown that NH₃ concentrationsclose to the litter surface (<20 cm), where the birds are exposed, canbe up to one order of magnitude higher than in the bulk house air (Lahavet al., 2008, supra). A significant departure is the concept of Lahav etal., 2008 of removing NH₃ using manifolds that extract only the airclose to the litter independent of the house ventilation system. Thepresent invention, using a membrane system, follows the same concept, inthat the NH₃ can be recovered near the litter with potential benefits tobird health and improved productivity, with the additional advantagethat NH₃ is passively removed.

Experiment 3

The third experiment tested the capacity of the membranes to trap NH₃ bybiologically enhancing the release of NH₃. To achieve this; organicnitrogen (approximately 10 grams of urea containing approximately 4.6grams of nitrogen) was added to a chamber containing litter at thebeginning of the experiment, resulting in a urea concentration ofapproximately 5% (w/w). This accounts for about twice the normal inputof nitrogen for an entire grow-out, in an average house (Nabor andBermudez, Poultry manure management and utilization problems andopportunities. Columbus, Ohio: Ohio State University, 1990). The addedurea acted as a substrate to microbiologically enhance NH₃ productionand volatilization from the litter. For comparison, a chamber withlitter and 0% urea addition was used as a control treatment.

Excess urea (approximately 5% total mass) was added to the litter todetermine how increased N input affected the NH₄-N mass potentiallyrecovered by the ePTFE system. The amount of urea added was equal toapproximately twice the N input of an average broiler over a typicalgrow-out period (about 42-56 days), assuming approximately 930 cm² (1ft²) of litter surface area is occupied per broiler. The abovecalculations assume that, oh a dry weight basis, an average broilerproduces approximately 37.5 g of manure daily, of which approximately0.75 g (approximately 2% of total mass) is in a nitrogenous form (Naberand Bermudez, 1990). Initially, the total N content of the litter in theapproximately 5% urea treatment chamber was approximately 16.39±0.86 g,with the urea accounting for approximately 42.8% (approximately 7.02 g)of the total N. For comparison, the litter from the non-amended (0%)treatment litter contained approximately 7.33±0.31 g of total N.

The addition of urea to the litter increased the recovery of NH₃(approximately 2287.4±9.2 mg) as compared to the non-amended litter(approximately 293.9±26.6 mg). The corresponding rate of daily NH₃capture per unit ePTFE surface area was approximately 10.5 g m⁻² d⁻¹ forthe enhanced urea treatment and approximately 1.3 g m⁻² d⁻¹ for thenon-amended litter (FIG. 8). The rate of NH₃ recovery in theapproximately 5% urea treatment (approximately 116.9 mg d⁻¹) wassignificantly (p<0.0001) higher than in the 0% treatments (approximately11.2 mg d⁻¹), according to regression analyses. These results indicatethat the ePTFE system had higher capacity to recover NH₃ than inprevious experiments (FIGS. 6 and 7; Tables 3 and 4), and that thelimitation in those experiments was the amount of available NH₃. Theconcentration of NH₄-N in the acidic solution after 21 days wasapproximately 7859±96 mg/L, or 0.79%.

In addition to NH₄-N reduction in the litter, the membrane treatmentalso reduced NH₃ concentrations in the air. Measurements of NH₃concentrations in the headspace air of the laboratory chamber after 7days showed approximately 1.2±0.1 mg L⁻¹ NH₃ in the membrane system andapproximately 17.5±0.2 mg L⁻¹ NH₃ in the control chamber withoutmembrane. This represents about a 93% reduction in the headspace NH₃concentrations in the membrane system.

The pH of the acidic solution in the 0% urea treatment was unchanged atday 21 compared to the beginning of the experiment, while the pH of theacidic solution from the approximately 5% urea treatment increased byabout 2 pH units (from 0 to 2). This increase in pH indicates about a99% reduction in the available protons (Lahav et al., Water Air SoilPollution, Volume 191, 183-197, 2008) in the approximately 5% ureatreatment after about 21 days as compared to the initial acidic solutionand that the acidic solution would have needed to be recharged torecover additional NH₃. Therefore, it is important to keep up with thecontinuous supply of protons in this type of system so that the acidityis not limiting effective NH₃ recovery. Fortunately, we can use the pHof the acidic solution as an indication of acid recharge needs.

Experiment 4

The fourth experiment determined if NH₃ could be recovered quickly fromthe litter through the use of chemical treatment in combination with theuse of membrane technology. To achieve this, amendments were added tothe litter to chemically enhance NH₃ production and volatilizationthrough the addition of hydrated lime, Ca(OH)₂ at four application ratesof approximately 0%, 0.4%, 2%, and 4% w/v. Hydrated lime was mixed withthe litter by vigorous shaking in a plastic bag and immediately placedin the chamber. Hydrated lime raised the pH of the litter (≧ to 10units) to convert available non-volatile NH₄-N into volatile NH₃-N.Hydrated lime has been historically used for disinfection and NH₃management of poultry litter (Shah et al., 2006, supra; Yushok and Bear,Poultry manure: Its preservation, deodorization, and disinfection. NewBrunswick: N.J. Agricultural Experiment Station, 1948).

Hydrated lime [Ca(OH)₂] was applied to the litter at three rates ofapproximately 0.4%, 2%, and 4% w/v to increase the pH of the litter torapidly transform NH₄-N into NH₃ gas and evaluate treatment timereduction compared to a control treatment (0% Ca(OH)₂ addition) (FIG. 9,Table 5). The addition of approximately 0.4%, 2%, and 4% Ca(OH)₂instantaneously increased the pH of the litter (approximately10.23±0.10, 12.69±01, and 12.81±0.10, respectively) as compared to thelitter without Ca(OH)₂ addition (approximately 8.96±0.02). As aconsequence, the NH₄-N content of the litter decreased quickly withinone day of chemical addition, from approximately 511.0±4.7 mg toapproximately 388.9±5.3, approximately 124.4±5.9, and approximately21.3±3.5 mg in the approximately 0.4%, 2%, and 4% Ca(OH)₂ treatments,respectively (FIG. 9B). Corresponding NH₄-N remaining in the litterafter one day was approximately 76.1%, approximately 24.3%, andapproximately 4.2%. After seven days, the NH₄-N content in the litter ofall three chemically amended treatments was zero, indicating completevolatilization. In contrast, the NH₄-N content remaining in the controland 0% treatment was approximately 602.0±1.3 and approximately 202.0±1.0mg, respectively (FIG. 9B), consistent with results obtained from thefirst and second experiments.

The increased NH₃ volatilization due to chemical addition significantlyaffected NH₃ recovery by the membrane system (FIG. 9A). Treatment timewas reduced from about 21 days to less than about seven days. Ammoniawas actively captured until days 7, 3, and 2 for the approximately 0.4%,2%, and 4% treatments, respectively, at which point the recovered NH₃reached a maximum and no significant additional NH₃ was captured in theacidic solution (FIG. 9A). In contrast, the treatment without hydratedlime addition slowly accumulated NH₃ in the acidic solution throughoutthe entire 21-day experiment. In terms of surface area of the membrane,the rates of NH₃ recovery were approximately 1.29, 4.94, 9.67, and 16.52g m⁻² d⁻¹ for the approximately 0%, 0.4%, 2%, and 4% respectively.Therefore, the speed of NH₃ recovery by the membranes can be enhanced byincreasing the pH of the litter, and commercially available hydratedlime is an effective chemical for this purpose.

The rapid flush of NH₃ by chemical addition exceeded the capacity of themembrane used in the bench-scale chamber, resulting in lower NH₃recoveries after seven days between approximately 68%-76% (Table 5). Forexample, the membrane capacity in the approximately 4% w/v limetreatments in the first two days was approximately 180 mg d⁻¹ (FIG. 9A),which is lower than the approximately 490 mg of NH₃ released the firstday after chemical addition (FIG. 9B). Therefore, it is important toconsider the NH₃ release dynamics to dimension the size of the membranesystem because NH₃ release may be substantially different with naturalor chemically enhanced systems.

TABLE 5 Mass balance, percent NH₃ recovery, and headspace NH₃concentrations from poultry litter seven days after addition of threedifferent hydrated lime rates Percent NH₃ Mass NH₃ Headspace NH₃Headspace Hydrated NH₄—N Mass Recovered in NH₃ ConcentrationConcentration Lime Loss from Litter Acid Trap Recovery without ePTFEwith ePTFE (w/v)^([a]) (mg)^([b]) (mg) (%) (mg L⁻¹) (mg L⁻¹) 0 202.0(1.0)^([c]) 146.3 (2.2) 72.4  8.8 (0.1)  0.2 (0.08) 0.4 511.0 (4.7)333.0 (5.5) 67.7 34.0 (1.4) 0.0 (0.0) 2 511.0 (4.7) 376.3 (4.9) 73.617.8 (1.4) 0.0 (0.0) 4 511.0 (4.7) 389.4 (2.1) 76.2 14.6 (1.6) 0.0 (0.0)LSD_(0.05) ^([d]) 14.55 63.93 7.24 0.02 ^([a])Percent total mass oflitter at the beginning of the experiment ^([b])Calculated bysubtracting mass of NH₄—N at day 7 from initial mass of NH₄—N in thelitter ^([c])Mean (standard error of the mean) of duplicate 2M KClextractions of litter ^([d])Least significant difference.

The use of a membrane system resulted in consistent decreases inheadspace NH₃ concentrations for all four treatments as compared to thecontrols without membranes (Table 5, Columns 5, 6). NH₃ concentrationsin the air were significantly (p<0.0001) reduced from approximately8.8-34.0 mg L⁻¹ to approximately 0.2-0.0 mg L⁻¹ (approximately97.7%-100% reduction).

An additional benefit of the use of hydrated lime is the disinfection ofthe poultry house. Lime has been shown to effectively destroy orinactivate bacterial and viral pathogens in poultry productionfacilities, including Salmonella enteritidis (Bennett et al., Effect oflime on Salmonella enteritidis survival in vitro. Journal of AppliedPoultry Research 12:65-68, 2003) and H5N1 virus (causative agent ofAvian Influenza; De Benedistis et al., Zoonoses Public Health 54:51-68,2007). Therefore, producers choosing to disinfect their houses usinglime could benefit from this membrane system by recovering the NH₃rapidly released from the litter upon lime application.

Example 2

Flat; microporous, hydrophobic, gas-permeable membranes 8 (FIG. 10) areillustrated in this example for recovery of ammonia (NH₃) volatilizedfrom poultry litter. A bench-scale prototype was used which comprised aplastic trough covered by a flat membrane of approximately 0.028 m²surface area, poultry litter (approximately 1 kg), and an acid solution(approximately 1 liter) within an enclosure (FIG. 10). This plastictrough covered with flat microporous, membrane (FIG. 15) consisted of aU-shaped PVC trough that measured about 11 cm width (top), 8 cm interiordepth, and 29 cm length (Model No. 400, NDS, Inc.). The depth of theacid solution 3 flowing inside was about 2.5 cm and the depth of themembrane air space 16 between the surface of the acid and the insider ofthe membrane was about 4 cm. The flat gas-permeable membrane 8 was madeof ePTFE with a thickness of 0.44 mm and a bubble point of 21 kPa(FL1001, Phillip Scientific, Inc.), and it was supported with a spunbondpolypropylene fabric (0.229 mm thickness) that faced the acid. A PVCframe cover (Model No. 241-1, NDS, Inc.) with large openings (7×1 cm)that were uniformly spaced (0.5 cm) was used to fasten the membraneassembly to the trough. The acid solution was recirculated at a rate ofapproximately 10 L d⁻¹. Hydrated lime (Ca(OH)₂) was applied at differentrates of approximately 0.1, 0.2, 0.5 and 2.0% w/v, to enhance ammoniavolatilization by increasing litter pH. Each treatment was run induplicate and a control treatment with no lime application (0% w/v) wasalso included. Changes in gaseous ammonia levels within the headspace ofthe enclosure and the levels of ammoniacal-N in the acid solution weremonitored over a 4-day period. As a result of liming, gaseous NH₃concentrations increased; rapidly in the headspace of the enclosureswithin approximately 6 hours for all Ca(OH)₂ treatments (FIG. 11), withhigher Ca(OH)₂ application rates resulting in higher measured NH₃concentrations in the air. As lime application rates increased, more NH₃gas went in the air. However, in all lime treatments, the NH₃ gasdecreased to a uniform level within 4 days with the membrane system(FIG. 11). As liming increases, more NH₃ is released into the air (FIG.11) and consequently more N is recovered (FIG. 12). Therefore the amountof N removed by the membrane from the air is proportional to theconcentration of ammonia in air. For example, after approximately oneday 17.1, 184.3, 329.8, 609.6, and 742.3 mg NH₃-N were recovered in theapproximately 0; 0.1, 0.2, 6:5, and 2.0% Ca(OH)₂ treatments,respectively. After two days, approximately 49.8, 284.3, 500.9, 927.2,and 1379.4 mg NH₃-N were recovered in the approximately 0, 0.1, 0.2,0.5, and 2.0% Ca(OH)₂ treatments, respectively. After three days,approximately 71.0, 329.7, 528.5, 1084.5, and 1452.8 mg NH₃-N wererecovered in the approximately 0, 0.1, 0.2, 0.5, and 2.0% Ca(OH)₂treatments, respectively. After four days, approximately 106.8, 382.4,598.2, 1266:2, and 1514.5 mg NH₃-N were recovered in the approximately0, 0.1, 0.2, 0.5, and 2.0% Ca(OH)₂ treatments, respectively. Most of therecovery (>73%) occurred in the first two days (FIG. 12). By day 4, ≧87%of the ammoniacal-N lost from the litter was recovered in the acidsolution for all treatments. These results demonstrated that flat,hydrophobic, gas-permeable membrane systems, can significantly reducegaseous NH₃ contamination of air from poultry litter and recover thevolatilized NH₃ in a liquid form.

Example 3

A field-scale prototype was used to further illustrate the ability of amicroporous hydrophobic, gas-permeable, membrane system 15 using flatmembranes to recover ammonia (NH₃) from NH₃ emitting source 6, i.e.,poultry litter, m (FIGS. 13 and 14). Poultry litter 6 (approximately32.5 kg) was placed inside an approximately 2.51 m³ enclosure 22 thatcontained a manifold system 17 with flat, hydrophobic, gas-permeablemembrane 8 (FIGS. 13 and 14). The manifold system consisted of fourtroughs 7 (FIGS. 13 and 15) as described in Example 2 but with a lengthof approximately 1.3 m each connected in series with an acid flow pipe18. The combined membrane surface area was approximately 0.4876 m².Approximately thirteen and a half L of an acid solution 3 wasrecirculated from the acid tank 1 to the membrane assembly 15 and backat a rate of approximately 27 L hr⁻¹. The experiment was done twice;once under normal conditions (no litter amendment), and the other withenhanced volatilization conditions using hydrated lime (Ca(OH)₂,approximately 2% w/v). The peak NH₃ concentration in the air (atapproximately 24 hrs) was approximately 915 and >2000 ppmv in the normaland enhanced volatilization treatments, respectively. Results in Table 6show that nearly all (>97.7%) of the NH₃ lost from the litter wasrecovered with the use of this invention. The liming increasedvolatilization of NH₃ from the litter (approximately 22.0% without limeand 100% with lime) and resulted in higher mass of N recovered (fromapproximately 29942 to approximately 48830 mg NH₃ in the approximately0% and approximately 2% treatments, respectively). Even though the NH₃was recovered efficiently in both situations, the average rate ofrecovery through the membrane (per unit surface area) was about 12%higher with the increased NH₃ availability due to liming (Table 6). Weconclude that the performance efficiency of NH₃ removal with thegas-permeable membrane system is consistent across a Wide range of NH₃volatilization conditions (normal or enhanced) in poultry manure.

TABLE 6 Recovery of ammonia using a field-scale flat membrane prototypesystem under normal and enhanced volatilization conditions^(a,b) NH₃Initial Final NH₃ Lost Recovered NH₃ Ca(OH)₂ NH₃ in NH₃ in from in theAcid NH₃ Recovery (w/v) Litter^(c) Litter^(c) Litter^(d,e) SolutionRecovery^(f) Rate^(g) % mg % mg NH₃ m⁻² d⁻¹ 0 139236 108590 30646 2994297.7 7011 2 48427 0 48427 48830 100.8 7867 ^(a)32.5 kg litter in a 2.51m³ enclosure ^(b)Days of experiment: 0% = 8.76 days; 2% = 12.73 days^(c)Measured using 2M KCl extraction method and colorimetry using anautoanalyzer (Peters et al., Ammonium nitrogen, p. 25-29, In J. Peters,ed. Recommended Methods of Manure Analysis. University of Wisconsinextension, Madison, WI., 2003) ^(d)Peak gaseous NH₃ concentration inair: 0% = 915 ppmv; 2% = >2000 ppmv ^(e)NH₃ Lost from Litter = InitialLitter NH₃ − Final Litter NH₃ ^(f)NH₃ Recovery = (NH₃ Recovered inAcid/NH₃ Lost from Litter) * 100 ^(g)Based on 0.4876 m² of flat membranesurface area per prototype

It will be clear to a person skilled in the art that the scope of thepresent invention is not limited to the examples discussed above, butthat various changes and modifications thereof are possible withoutdeparting from the scope Index of the invention as defined in theappended claims.

INDEX OF THE ELEMENTS

-   -   1. Acid tank or reservoir    -   3. Acid Solution    -   4. Fluid Pump    -   4A. Intake End    -   4B. Discharge End    -   6. NH₃ Emitting Source    -   7. Trough covered with flat membrane    -   8. Hydrophobic gas-permeable membrane    -   8A. Outer Surface of Membrane    -   8B. Inner Surface of Membrane    -   9. Membrane Pores    -   10. Hollow Inferior of Tubular Membrane    -   11. Intake Flow Line    -   12. Discharge Flow Line    -   15. Membrane Assembly/System    -   16. Membrane Air Space between the Inner Surface of Membrane and        Surface of the Acid Solution.    -   17. Membrane Manifold System    -   18. Acid flow Pipes    -   20. Ammonia Capture System    -   22. Chamber/Enclosure    -   26. Floor    -   40 Membrane Assembly Entry Opening    -   42. Membrane Assembly Exit Opening

1. An ammonia gas capture system for reducing the ammonia concentrationwithin an enclosure, comprising: A membrane assembly having a permeablemembrane wherein said permeable membrane allows for diffusion of ammoniagas concentrated outside said membrane's outer surface through themembrane wherein said ammonia gas contacts an acid supply, a reservoircontaining an acid supply wherein in said reservoir pumps said acidsupply through said membrane assembly; and a delivery system fordelivering acid from the reservoir to said membrane assembly in order tochemically change the ammonia gas to ammonium salts and for carrying thesalts to and said reservoir.
 2. The system according to claim 1 whereinsaid system further comprises, a pump having an intake end and dischargeend, and at least two hollow tubes having distal and proximal ends, afirst tube having one end attached to the discharge end of the pump anda second end attached to an entry opening of said membrane assembly andsaid second tube having a first end attached to an exit opening of saidmembrane assembly and a second end disposed above or in said reservoirfor discharging ammonium salts to said reservoir.
 3. The system of claim2 wherein said membrane assembly includes a tubular membrane with ahentry and exit opening wherein said first and second tubes are attachedto said entry and exit openings of said membrane.
 4. The system of claim2 wherein said membrane assembly includes a flat membrane and an acidcontaining trough wherein said membrane is in communication with saidtrough with said trough having an entry and exit opening and said firstand second tubes are attached to said entry and exit openings of saidtrough.
 4. The system according to claim 1 wherein said membraneassembly is suspended above a floor covered with a gaseous N producingsubstance.
 5. The system according to claim 1 wherein said membraneassembly is located beneath a floor covered with a gaseous N producingsubstance.
 6. The system according to claim 1 wherein said membraneassembly is located on a surface covered with a gaseous N producingsubstance.
 7. The system according to claim 1 wherein said acid isselected from the group consisting of organic acids, mineral acids,precursors of organic acid and mineral acids and mixtures thereof. 8.The system according to claim 7 wherein said organic acid is selectedfrom the group consisting of citric, oxalic; lactic, or mixturesthereof.
 9. The system according to claim 7 wherein said mineral acid isselected from the group consisting of sulfuric, hydrochloric, nitric,phosphoric, and mixtures thereof.
 10. The system according to claim 7wherein said precursor of said acids are selected from the groupconsisting of sodium bisulfate, sulfur, corn silage, molasses/andcarbohydrates or mixtures thereof.
 11. A method for producing ammoniumsalt from an enclosure, comprising: capturing ammonia gas within theconfines of a membrane assembly haying a gas-permeable membrane, saidgas generated substantially from material containing ammonium,contacting said ammonia gas with an acid solution in said membraneassembly wherein said acid is in fluid communication with said gas toproduce ammonium salts; and transporting the salts for collection to areservoir in fluid communication with said membrane assembly.
 12. Themethod of claim 11 wherein said membrane assembly includes a tubulargas-permeable membrane.
 13. The method of claim 11 wherein said membraneassembly includes a flat membrane and a trough containing acid whereinsaid membrane is in communication with said trough.
 14. The methodaccording to 11 wherein said ammonia gas is captured below the floor ofsaid enclosure.
 15. The method according to claim 11 wherein saidammonia gas is captured on the floor of said enclosure.
 16. The methodaccording to 11 wherein said ammonia gas is captured above the floor ofsaid enclosure.
 17. The method according to claim 11 wherein said acidis selected from the group consisting of organic acids, mineral acids,precursors of mineral and organic acids, and mixtures thereof.
 18. Theaccording to claim 17 wherein said organic acids is selected from thegroup consisting of citric, oxalic, lactic, and mixtures thereof. 19.The method of claim 17 wherein said mineral acids is selected from thegroup consisting of sulfuric, hydrochloric, nitric, phosphoric, andmixtures thereof.
 20. The method of claim 17 wherein in said precursorsare selected from the group consisting of sodium bisulfate, sulfur, cornsilage, molasses, and carbohydrates.
 21. The method according to claim11 further including adding chemical amendments to said material toexpedite the production of ammonia gas for capture by said gas-permeablemembrane.
 22. The method according to claim 21 wherein said chemicalamendment increases the pH of said material.
 23. The method according toclaim 21 wherein the chemical amendment is selected from the groupconsisting of calcium hydroxide, magnesium hydroxide, calcium oxide,magnesium oxide, dolomitic lime, sodium hydroxide, potassium hydroxide,and mixtures thereof.